Dock shelters are employed to provide a weather seal between the rear end of a truck body and a loading dock. In general, the conventional dock shelter includes a pair of vertical side pads formed of a compressible material which are located on either side of the doorway in the dock. Extending across the upper end of the doorway is a compressible head pad. As the truck back toward the dock the rear end of the truck body engages the pads, compressing them and providing a weather seal between the truck body and the dock.
As the vertical height of the roof of a truck body can vary considerably, movable head pads have been employed to accommodate the variance in roof height. A mechanism for adjusting the vertical height of the head pad is shown in U.S. Pat. No. 3,230,675. In that patent elongated guide rods are attached to opposite sides of the head pad and the guide rods slide within tracks on a fixed frame attached to the dock. Counterbalancing weights are connected through cables to opposite ends of the head pad to counterbalance the weihgt of the head pad. The head pad is raised and lowered manually and the counterbalancing weights will retain the head pad in the desired vertical position.
The adjustable head pad mechanism as shown in U.S. Pat. No. 3,230,675 has certain disadvantages. As each side of the head pad is connected to an independent counterbalancing mechanism, there is a tendency for the head pad to rack or cock as it is moved vertically which can result in jamming of the guide mechanism. Furthermore, the swinging counterweights are exposed on the deck wall and can be a hazard to workers.
It has been found that in service, the weight of the head pad may change considerable due to the absorption of water, and with the construction shown in the aforementioned patent, the counterbalancing weights cannot be readily changed to compensate for the change in weight of the head pad.
As a further difficulty, with the construction shown in the aforementioned patent, there is no mechanism for precise leveling of the head pad on installation, other than changing the magnitude of the respective counterweights.